John Chrysostom

"For this cause many among you are weak and sickly, and not a few sleep." Here he no longer brings his examples from others as he did in the case of the idol-sacrifices, relating the ancient histories and the chastisements in the wilderness, but from the Corinthians themselves; which also made the discourse apt to strike them more keenly. …

Homily on 1 Corinthians 28 ↗

Theophylact of Ohrid

Take the proof of what has been said from what happens among you. For it is because many partake unworthily that cases of untimely death and prolonged illnesses occur. But do those who reach the deepest old age without experiencing illness no longer sin? They do sin. But for those who approach unworthily, not only these present punishments await, but even more severe ones in the other life. And we would not be punished even here if we did not sin, as he continues.

Commentary on 1 Corinthians ↗

Thomas Aquinas

Then when he says, That is why, he clarifies the reason he gave with a sign. First, he mentions the sign; secondly, he assigns the cause of that sign (v. 31). In regard to the first it should be noted that, as Augustine says in The City of God: "If God punished every sin with a penalty now, it would be thought that nothing was left for the final judgment." Again, if He punished no sin now, it would be believed that there is no divine providence. …

Commentary on 1 Corinthians ↗